Muscular dystrophies are a relatively common group of inherited degenerative muscle disease. Most types are caused by mutations in genes coding for membrance associated proteins in muscle. Duchenne muscular dystrophy (DMD) and limb-girdle muscular dystrophy (LGMD) often manifest themselves in young ages and lead to early morbidity with no currently available effective treatment. These diseases are recessive, loss-of- function of the corresponding gene product, which makes them suitable for gene replacement therapy. Recombinant adeno-associate virus (rAAV) is one promising gene replacement vector based on defective human parvoviruses. The rAAV system has attracted attention due to its non- pathogenicity, genomic integration, transduction of quiescent cells, and apparent lack of cellular immune reactions. In contrast to other viral vectors, rAAV is capable of efficiently bypassing the myofiber basal lamina and transducing mature muscle cells. We have demonstrated that rAAV vectors harboring a foreign gene can achieve highly efficient and sustained gene expression in mature muscle of immunocompetent animals for more than 1.5 years without detectable toxicity. Recently, significant improvement in vector production methodology has made it possible to generate high titer and high quality rAAV vectors completely free of helper adenovirus contamination. However, no experiments using rAAV vectors to restore the functional deficits in muscle tissue itself have been reported to date. Here, we propose to take advantage of rAAV vector system, to test two therapeutic genes (delta-sarcoglycan and a highly truncated dystrophin), under the control of two different promoter systems (viral/CMV or muscle- specific/MCK), in two relevant animal models of muscular dystrophies (Bio14.6 hamster for LGMD and mdx mouse for DMD). Two distinct vector delivery methods, local intramuscular infection versus systemic delivery will be utilized. We have the following three hypotheses to be tested. 1): muscle deficient in delta-sarcoglycan can be functionally rescued by genetic complementation using intramuscular AAV vector injection in the LGMD hamster model. 2) systemic delivery of the delta-sarcoglycan gene can be mediated by rAAV vectors through intra-artery or intra-ventricle injection. 3) a dystrophin mini-gene lacking the central rod domain will improve the function of dystrophin-deficient muscle when delivered into dystrophic mdx mice by AAV vectors.